LCST in poly(N-isopropylacrylamide) copolymers: high resolution proton NMRinvestigations

A series of copolymers of N-isopropylacrylamide (NIPA) and acryloyl amino a cids were synthesized and conjugated with p-aminobenzamidine (PABA). The va lues of lower critical solution temperatures (LCSTs) of these polymers esti mated by H-1 NMR were in agreement with those estimated by the turbidometri c methods. The apparent shifts in the peak positions for the polymer with i ncreasing temperature reported in the past are shown to be artifacts result ing from the deuterium lock experiment. The H-1-H-1 NOESY experiments were carried out to distinguish the interactions between the protons in: (a) 6-a mino caproic acid (6ACA) and NIPA and (b) PABA and NIPA. These explain the variation in the LCST of the polymers based on the contributions of the two monomers to the magnitude of the polymer-polymer interactions. The finding s are further supported by proton spin-lattice relaxation time measurements . (C) 2000 Elsevier Science Ltd. All rights reserved.